Field of the Invention
The invention relates to a pressure sensor having an optical waveguide, which has an optical fiber with a refractive index of n1.
Pressure sensors such as these are disclosed, for example, in German Patent DE 197 21 341 C2, German Published, Non-Prosecuted Patent Application DE 42 36 742 A1, and German Published, Non-Prosecuted Patent Application DE 36 03 934 A1. In the known pressure sensors, light is fed into the optical waveguide and the attenuation of the light is used as a measure of the pressure load on the optical waveguide. This makes use of the characteristic of the optical waveguide that, when it is mechanically loaded, the optical waveguide is curved or bent so that its optical characteristic and, hence, its attenuation behavior, are changed. In particular, use is, in this case, made of the effect that the physical boundary condition for total internal reflection of the light within the optical waveguide is no longer satisfied when the optical waveguide is bent to a critical extent. Here, the majority of the light is emitted from the fiber. This leads to attenuation, which is detected by a suitable sensor and is used as a measure of the pressure load. One disadvantage in this case is that the pressure sensor has only a low level of sensitivity because the pressure sensor responds only to predetermined bending of the optical waveguide.
Pressure sensors such as these, in which the optical waveguide is deformed when pressure is applied, are also disclosed in U.S. Pat. No. 4,915,473 to Haese et al., JP 59128009, and German Published, Non-Prosecuted Patent Application DE 34 43 949 A1.
U.S. Pat. No. 4,735,212 to Cohen discloses a medical catheter with an internal optical waveguide. To detect a pressure, foamed sub-elements are incorporated, in particular, in the sheath or casing at predetermined points on the catheter, and are intended to transmit pressure to the optical waveguide, which is free of cladding only in these sub-areas.